Three-Dimensional Mesoporous Polyindole Architectures for Supercapacitor Applications

Recently, polyindole (PIN) has quickly started to gain research interest in the field of energy storage applications. Here, we developed a three-dimensional (3D) PIN gel for the first time without using either additives or cross-linkers to explore its efficacy as a supercapacitor. The PIN aerogel obtained by freeze-drying the 3D PIN gel exhibits a larger surface area, enhanced electronic conductivity, and appropriate mechanical properties compared to conventionally synthesized PIN powder. The PIN aerogel is also capable of delivering an improved capacitance of 168 F g –1 at a current density of 0.5 A g –1 . Further, we have also demonstrated that PIN can be used as a cross-linking agent in the development of a PIN/graphene hydrogel (PG hydrogel). The PG hydrogel was freeze-dried to obtain PIN/graphene aerogels (PG aerogels). With improved surface areas and 3D porous nanostructures, the PG aerogels demonstrated their potential as high-performance supercapacitor electrodes with a high specific capacitance of ∼399 F g –1 at 0.5 A g –1, better rate capability, and long-term cyclic stability (∼92% capacitance retention after 2000 cycles) in a three-electrode system. Besides, we also report the fabrication of a PG aerogel∥PG aerogel symmetric supercapacitor (SSC) of a two-electrode configuration, which manifests a favorable C sp of 63 F g –1 at 0.5 A g –1 and retains a stability of 99.8% even after 2000 cycles. This SSC device shows a significant energy density of 28.35 Wh kg –1 at a power density of 497.85 W kg –1 . The self-aggregation of PIN and the interaction of PIN with graphene was assessed using molecular dynamics (MD) simulations. The MD simulation results were found to be in good agreement with the experimental observations. Overall, our findings evidence that PIN can form 3D architectures in virgin nature and composite with graphene and thus has important implications for future material design of PIN-based electrochemical energy storage devices.